Fair Value Measurements (Fair Values of Assets and Liabilities (Significant Unobservable Level 3 Inputs Nonrecurring Basis)) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2019
Commercial loans held for sale | Commercial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair value measurements nonrecurring assets	$ 16
Commercial and Industrial Loans | Commercial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair value measurements nonrecurring assets	93	$ 169
Commercial mortgage loans | Commercial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair value measurements nonrecurring assets	2	12
Commercial Leases
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair value measurements nonrecurring assets	14
Commercial Leases | Commercial
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair value measurements nonrecurring assets		20
OREO Property
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair value measurements nonrecurring assets	20	13
Bank premises and equipment
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair value measurements nonrecurring assets	32	27
Operating lease equipment
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair value measurements nonrecurring assets	0	6
Private equity investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Comparable company analysis, fair value	3	$ 2
Other assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair value measurements nonrecurring assets	$ 2
Minimum | Private equity investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Liquidity discount	0.00%
Maximum | Private equity investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Liquidity discount	43.00%
Weighted-average | Commercial loans held for sale
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Cost to sell	10.00%
Weighted-average | Private equity investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Liquidity discount	12.90%